1. Field of the Invention
The present invention relates to a touch sensing device and method of identifying the touched position, and more particularly to touch coordinates calculation for a capacitive touch sensing device.
2. Description of the Related Art
In recent years, capacitive touch screen have been used in a large number of devices. U.S. Pat. No. 7,030,860B1 discloses a structure in which a plurality of X-electrodes aligned in an X-direction and a plurality of Y-electrodes aligned in a Y-direction are formed on a single glass substrate as a structure of the capacitive touch screen. JP2009-244958A discloses a structure of a touch sensor in which parts of liquid crystal display elements form Y-electrodes, and X-electrodes are disposed on a glass for liquid crystal display. The touch sensor disclosed in JP2009-244958A does not require the sheet only for the touch sensor. In the touch sensors disclosed in those publications, touch coordinates are obtained according to a detected signal corresponding to a variation in a mutual capacitance between the X-electrode and the Y-electrode due to a finger touch in each combination of the X-electrodes and the Y-electrodes.
As a method for obtaining the touch coordinates, for example, there is a method for obtaining, as the touched position, the centroid calculated with the detected signal as a weight at a center position of a cross portion of each combination of the X-electrodes and the Y-electrodes. The detected signal corresponding to a mutual capacitance variation in each combination of the X-electrodes and the Y-electrodes.
It is conceivable that, when the screen is touched by a finger, there are measurement portions (the cross portion of each combination of the X-electrode and the Y-electrode) in a given range where the detected signal corresponding to a variation in the mutual capacitance is obtained. On the other hand, when the finger touches an end of the above-mentioned sensing area, the detected signal which would be obtained when measurement portions are present outside of the end of the sensing area is not obtained. For that reason, in a case where the end of the sensing area is touched by the finger, a gap between touch coordinates by the centroid calculation, and the actually touched coordinates becomes larger than a case where a neighborhood of the center of the sensing area is touched. Also, a method for correcting the calculated coordinates with some calculation formula is also proposed. However, this method has a limited improvement in a precision of the coordinates.